In the analysis and study of body fluids, the fluids to be studied are generally diluted in order to carry out the analytical procedures on diluted samples. In many cases, the diluting operation is performed manually, using a standard calibrated pipette. This manual procedure is time consuming and tedious in addition to presenting a great opportunity for error, especially where a high degree of skill has not been attained by the technician, and where a high speed of operation is necessary or desirable. Mechanical diluters have been used successfully for a number of years. Examples of such devices are shown and described in U.S. Pat. Nos. 3,138,290 and 3,138,294.
Efforts have been made to develop semiautomatic electromechanical devices for performing diluting operations. One such device is shown and described in U.S. Pat. No. 3,446,400, issued May 27, 1969 to J. C. Hobbs II et al. Although semiautomatic electromechanical diluters have been used successfully for a number of years, these devices tend to be cumbersome, and complicated. In the Hobbs device, a motor driven eccentric and yoke assembly are arranged to shift downwardly and upwardly the piston of a fixed volume diluent chamber for drawing and discharging a measured amount of diluent. As the yoke assembly approaches its lower position, it engages and drives downwardly the piston assembly of a sample chamber communicating with an uncalibrated pipette, thus drawing a volume of sample into the pipette. As the yoke assembly is then upwardly moved, the sample and diluent are discharged through the pipette.
The ratio of sample volume to diluent volume must be precisely maintained in order to allow correct statistical evaluation and analysis of the diluted samples. Movement of the piston assembly in the sample chamber must be precisely synchronized with movement of the yoke assembly and the piston of the fixed volume diluent chamber in order to achieve a precise ratio of sample and diluent. This synchronization is achieved via adjustable stops attached to the piston assembly of the sample chamber and to adjustments possible on the yoke assembly itself. A loosening of these adjustments, or a wearing away of any of the parts so as to produce greater movement of one piston relative to the other in response to movement of the yoke, will cause a change in ratio of sample volume to diluent volume. Frequent adjustments of these limits and stops have been required in order to maintain a reasonable degree of accuracy for the mechanical diluter. These frequent adjustments are unnecessarily time consuming and expensive, as well as reducing the amount of time during which the mechanical diluter may be employed and creating a serious and substantial source of error.
Semiautomatic electromechanical diluters designed to satisfy most user requirements are further complicated in that they must provide a plurality of different precise dilution ratios by simple switch selection. In general, prior efforts to develop a diluter which may be operated to selectively provide one of a plurality of precise dilution ratios have been unsuccessful or have resulted in a device such as described above and having all of the problems noted above.